Calcium sulfonate or calcium hydrocarbyl sulfate accelerator for amine cure of epoxy resins

Accelerator Activity of Calcium Sulfonate Compared with Calcium Nitrate.

A mixture (Accelerator A) was prepared by mixing 59 parts by weight of Ca(NO 3 ) 2 .4H 2 O with 41 parts by weight of polyethylene glycol 400 and stirring until the mixture became a homogeneous liquid. Accelerator A, Stepan Ninate 401 calcium dodecylbenzenesulfonate solution and salicylic acid (the latter predissolved in 2-methyl-1,5-pentanediamine) were then mixed with EPON® Resin 828 and 2-methyl-1,5-pentanediamine in the indicated proportions and the mixtures (mass 75-80g) were then tested for gel time (with no external heat applied) in a Shyodu gel timer with a rotating probe, and also on thin film gel plates at 90° C. and 120° C. Additional mixtures of the epoxy resin with 2-methyl-1,5-pentanediamine and the accelerators were prepared and poured into casting molds made of two 1/8 (3.18 mm) thick glass plates separated by a 1/8" (3.18 mm) thick polytetrafluoroethylene spacer. The castings were allowed to cure overnight at room temperature and were then cured for 2 hours at 80° C. the following day. Physical properties of the castings were determined and are shown in Table 1.

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1 2 3 4 5 6 7

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Composition:

Epoxy Resin, grams 128 128 128 128 128 128 128

epoxy equivalents 0.681 0.681 0.681 0.681 0.681 0,691 0.681

2-methyl-1,5-pentanediamine, grams

22 22 22 22 22 22 22

NH equiv. 0.757 0.757 0.757 0.757 0.757 0.757 0.751

Accelerator A, grams 1.28 1.92

Ninate 401, grams 1.28 2.56 3.84

Salicylic acid, grams (predissolved in amine) 2.56

NH/epoxy ratio, eq/eq

1.11 1.11 1.11 1.11 1.11 1.11 1.11

Uncured properties:

Shyodu gel time, min.

88.5 10.2 7.6 33.3 12.0 10.7 22.3

Thin film gel time, sec., 90° C.

340 180 280 180 170 200

120° C. 95 25 72 46 39 53

Cured properties:

Rheometrics tan δ peak, °C.

113 110 117 107 105 105 116

R.T. dry flexural (ASTM D-790)

Yield strength, MPa 102 ± 1

104 ± 1

106 ± 1

105 ± 1

105 ± 1

105 ± 1

116 ± 1

Tangent modulus, GPa 2.66 ± 0.02

2.67 ± 0.03

2.73 ± 0.03

2.70 ± 0.02

2.69 ± 0.03

2.67

2.96 ± 0.03

Break elongation, % ≧6.5

≧6.5

≧6.5

≧6.4

≧6.5

≧6.4

≧6.5

Compact tension fracture toughness, K.sub.q,

1.94 ± 0.11

1.94 ± 0.09

1.76 ± 0.14

1.88 ± 0.15

1.83 ± 0.09

1.75

1.51 ± 0.07

MPa-m.sup.1/2 (ASTM E 399-83)

93° C. H.sub.2 O pickup, %: 1 day

1.74

2 weeks 2.64

Room temp. methyl ethyl ketone pickup, %:

1 day 0.33 0.25 0.23 0.29 0.29 0.20 0.36

2 weeks 3.16 5.01 4.48 6.32 5.49 disint.

6.27

Room temp. CH.sub.2 Cl.sub. 2 pickup, %, 1 day

disint.

disint.

disint.

disint.

disint.

disint.

disint.

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From Table 1 above can be seen the accelerator effect of the Ninate 401. On a weight basis, Ninate 401 is a weaker accelerator than Accelerator A but slightly stronger than salicylic acid. On the basis of calcium content, however, Ninate 401 (3.73% calcium by weight) is almost as active as the calcium nitrate-based Accelerator A (10% calcium by weight).

Comparison of Stability of Calcium Sulfonate Accelerator and Calcium Nitrate Accelerator as Solutions in 2-Methyl-1,5-Pentanediamine.

Mixtures of Ninate 401 (or Accelerator A), with 2-methyl-1,5-pentanediamine and water were prepared in small vials as shown in Table 2 below.

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Mixture #

1 2 3 4 5 6 7 8

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2-methyl-1,5-

5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5

pentane-

diamine,

grams

Accelerator

0.96 0.96 0.96 0.96

A, grams

Ninate 401, 0.96 0.96 0.96 0.96

grams

Water, grams 0.11 0.30 1.00 0.11 0.30 1.00

Precipitate

Yes Yes Yes Yes No No No No

after 1 day?

Precipitate

Yes Yes Yes Yes No No No Yes

after 2

months?

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From Table 2 can be seen that the mixtures containing Ninate 401 showed much greater resistance to precipitate formation, even in the presence of water. All of the mixtures containing Accelerator A showed heavy precipitate formation after 1 day, whereas all the Ninate 401 mixtures (except the one with the highest amount of added water) were free of precipitate even after 2 months. Table 3 below shows that Ninate 401/2-methyl-1,5pentanediamine mixtures showed no loss of accelerator activity after storage for six days, when the amine mixtures were mixed with EPON Resin 828 and gel tests were run as in Example 1.

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Mixture # 1 2

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2-methyl-1,5-pentanediamine, grams

55 55

Ninate 401, grams 3.2 9.6

Amount of above amine mixture used for gel

11.64 12.92

tests, g

Amount of EPON ® Resin 828 used for

64 64

gel tests, g

Shyodu gel time, min., initially

33.3 10.7

after 6 days 25.9 9.4

Thin film gel time, sec., initially, 90° C.

280 170

120° C. 72 39

Thin film gel time, sec., after 6 days, 90° C.

290 175

120° C. 70 25

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Comparison of Calcium Naphthenate with Accelerator A and Ninate 401 as an Accelerator for Aliphatic Amine Cure of Epoxies.

A calcium naphthenate mixture (Nuodex) containing 10% calcium was tested as an alternative accelerator to Accelerator A and Ninate 401 for the cure of EPON Resin 828 with 2-methyl-1,5-pentanediamine, as shown in Table 4 below. One can see from the results shown below that calcium naphthenate had little or no accelerator activity, even though it was soluble in the resin/amine mixture. This suggests that calcium salts of anions with relatively high basicity and nucleophilicity, such as most carboxylate anions, may not be generally effective as accelerators.

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Mixture # 1 2 3

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EPON ® Resin 828, grams

64 64 64

2-methyl-1,5-pentanediamine, grams

11 11 11

Calcium naphthenate, grams 0.64 1.28

Shyodu gel time, min.

88.5 80.5 92.9

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Acceleration of Amine Cure of Epoxy Resin using Ninate 401 anti Other Accelerators.

Mixtures of EPON Resin 828 with Amicure PACM (mixture of isomers of bis(4-aminocyclohexyl)methane) and accelerators were prepared and Shyodu gel time was determined as in previous examples. Table 5 shows the relative effect of these materials as accelerators.

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Mixture # 1 2 3 4 5

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EPON ® Resin 828, grams

58 58 58 58 58

Amicure PACM, grams

17 17 17 17 17

Accelerator A, grams 0.58

Ninate 401, grams 0.59 1.16

Salicylic acid, grams 0.59

(predissolved in amine)

Shyodu gel time, min.

202 24.3 126.3 68.2 81.1

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